The demand for liquid crystal color displays has been increasing rapidly in recent years in conjunction with the advances being made in personal computers in general and portable personal computers in particular. In responding to this demand, high priority is now being given to establishing means for supplying beautiful displays at reasonable cost. At the same time, in recent years, protecting the environment has become a big issue, and high priority is being given to making improvements in or converting to processes that will reduce the impact on the environment.
A number of methods are known conventionally for manufacturing color filters. One example is to pattern a light blocking material that is a thin film of chromium by photolithography and etching to form a black matrix. Then red, green, and blue photosensitive resins are applied to the gaps in that black matrix, one color at a time, by a spin coating method or the like, after which patterning is done by photolithography. In that way a color matrix can be configured wherein red, green, and blue coloring layers are deployed adjacent to each other. With this manufacturing method, however, the photolithographic process must be repeated for each of the red, green, and blue colors. Not only so, but the elimination of unneeded portions when patterning each color results in losses of photosensitive resist material. Thus this method tends to have a high impact on the environment and produce high-cost color filters.
In Japanese Patent Laid-Open Publication No. S59-75205, a method is proposed wherein an ink jet method is employed. In this method, ink coating gap partitions are formed in a matrix pattern on a transparent substrate, using a material that exhibits low ink wettability, after which a coloring layer is formed by applying non-photosensitive coloring materials inside the partitions using an ink jet method. By using this manufacturing method, the tediousness of the photolithographic processes can be alleviated, and it has become possible to reduce color material losses. Subsequently, many color filter manufacturing methods have been proposed which employ non-photosensitive coloring material application processes based on an ink jet method.
In one example, a chromium film is formed on a glass substrate using a sputtering film-forming method, this is etched in a prescribed pattern to form openings (pixels or light-transmitting areas), and those openings are filled with ink drops, thus manufacturing a color filter.
In many methods, a black photosensitive resin composition is used as the light blocking material, and, thereby, a bank layer is formed to partition the areas that are to be coated with coloring materials in a matrix pattern. In these methods, the surface of the bank layer that functions as a black matrix is imparted with an ink repelling quality, and color mixing caused by bank layer overflows in the color material application process is prevented.
In the art disclosed in Japanese Patent Laid-Open Publication No. H4-195102, Japanese Patent Laid-Open Publication No. H7-35915, Japanese Patent Laid-Open Publication No. H7-35917, and Japanese Patent Laid-Open Publication No. H10-142418, for example, in every case, a difference in ink wettability is elicited between the bank layer and the transparent substrate by the selection of the resin materials configuring the black matrix and by surface processing done on the surface of the transparent substrate in areas where coloring materials are applied.
When a chromium film is formed by a sputtering film forming method to form the banks, however, the limitation on the film thickness is about 0.2μ, and banks having sufficient height (0.5μ to 10μ) for ink filling cannot be formed. Also, when the interiors of openings enclosed by banks are filled with ink drops by the ink jet method, it is necessary to prevent the ink drops from crossing over the banks so that they overflow into neighboring pixels, making it necessary to impart ink affinity to the substrate and ink repellency to the banks. Hence it is preferable that the upper parts of the banks be configured by materials such as organic materials that may be readily subjected to ink repellency treatment.
Thereupon, in view of the problems noted in the foregoing, an object of the present invention is to provide color filters and liquid crystal elements comprising banks that are ideal for methods of manufacturing color filters by filling banks with ink by the ink jet method. Another object thereof is to provide a color filter manufacturing method well suited to the ink jet method.
When, on the other hand, a photosensitive black resin composition is used for the light blocking material in forming the black matrix, it is very difficult to obtain the right balance between light transmissivity and resin hardness. In actual practice, film thickness variation in the black matrix layer, which functions as the bank layer, is unavoidable because the film thickness is large. When a negative resist is used, for example, where the film thickness is thick, portions develop in the lithographic process that do not adequately transmit light, whereupon unhardened portions remain. When such unhardened portions as these are present, it is sometimes not possible to obtain sufficient film strength in the black matrix layer. Places where the film thickness is thin in the black matrix layer, on the other hand, become semi-transparent so that adequate light blocking properties are not obtained, sometimes leading to the occurrence of light leakage.
In recent years, color filters have become increasingly more high precision, making it necessary to form very fine red, green, and blue pixels that are a few tens of μ square, with good coloring material bonding, while minimizing color tone variation. With the conventional art, however, making the contact angles of the resin banks that demarcate and partition the pixels on the large size becomes a cause of pixel bonding flaws due to resin components spattering about the periphery. In methods which combine such dry etching processes as UV irradiation, plasma etching, and laser ablation for the purpose of preventing such bonding flaws, selectively processing only the gap portions where the ink is to be deployed becomes increasingly difficult the finer the patterns become. For this reason, the bank portions also end up getting processed at the same time, which only causes the contact angle to decline significantly. That is, attempts to make the difference in contact angle between the transparent substrate surface portion where the coloring material of the increasingly minute pixels adheres and the black resin banks that demarcate those portions particularly large are not very effective, especially in view of the high degree of technical difficulty involved.
Forming the thicknesses wherewith coloring materials adhere evenly in order to minimize variation in color tone in even more minute pixels is a very important process in determining color filter quality, but such processes are not elucidated in the prior art.
There is also nothing elucidated in the prior art about techniques for forming adjacent red, green, and blue deployments in such minute pixels, simultaneously, and without ink color mixing.
The present invention, devised for the purpose of radically resolving such technical difficulties inherent in the prior art, provides a method wherewith inks, as the coloring material, can be efficiently deployed in light blocking material matrix gaps by the ink jet method. Not only so, but a method is provided wherewith, because the ink film thickness is made uniform and given high bonding properties, high-contrast color filters are manufactured without pixel flaws or color tone irregularities. Another object is to provide a manufacturing method for liquid crystal display devices wherein such color filters are incorporated.
Another object is to provide color filters that comprise both light blocking regions having adequate light blocking properties and transparent regions wherein there is no color mixing, together with a manufacturing method therefor.
Yet another object of the present invention is to provide electro-optical devices and electronic equipment having such color filters as those described in the foregoing.